Mechanical Weakness Of The Nankai Accretionary Prism: Insights From V-P Measurements Of Drill Cuttings

The relationship between P-wave velocity (V-p) and unconfined compressive strength (C-0) can be used to estimate in situ rock strength and stresses at depth in subduction zones. However, few reliable data on the V-p-C-0 relationship in deep accretionary prism sediments are available. Here, we determined the V-p-C-0 relationship down to similar to 3.2 km in the Nankai accretionary prism from V-p measurements and indentation tests of drill cuttings retrieved from International Ocean Discovery Program Site C0002. In our results, the Nankai accretionary prism sediments tended to be weaker compared with estimates obtained by using other empirically determined V-p-C-0 relationships. We also examined the relationship between V-p and porosity in the accretionary prism. The V-p-porosity relationship obtained by using only data of Nankai accretionary prism sediments showed that V-p generally increased with decreasing porosity; this result is consistent with published V-p-porosity relationships for Nankai Trough sediments. The empirical relationships derived in this study should improve estimates of stress state, pore pressure, and fault strength in the Nankai accretionary prism.